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Overview

Fostex T50RP v2

The Fostex T50RP is an orthodynamic-type headphone introduced in 2002 and intended for professional audio applications. It was the first production isodynamic/orthodynamic/planar-magnetic headphone to take advantage of modern neodymium-iron-boron magnets, and makes extensive use of finite element analysis in the design of its magnetic circuit. The design features user-replaceable (in a professional environment) diaphragms and a detachable cable compatible with all Fostex T20 and T40 models made since 1986, because it uses an enclosure or chassis that is very similar to that of the RP headphones Fostex has been making since 1986.

The T50RP has nothing in common with the earlier (1978) T50 (v1 or v2) aside from its operating principle. Where the earlier headphone had audiophile pretensions, the T50RP is strictly meant as a professional tool. However, the advanced driver that was designed for it is very capable and with modifications (some of which require radical reworking of the entire headset), the T50RP can be a satisfying enthusiast headphone. It has the twin virtues of being easily available and remarkably affordable (~$75 street, as of 2012). In many ways, it has become the vanguard headphone of the ortho/isodynamic-enthusiast movement.

There are two versions: early production (2002-2007) with thick but very lightweight earpads with a flat face, acoustically very permeable (and as a result the headphone has very little bass), and later production, from 2007 on, which has a thinner, much denser, rounded-face earpad (see photo) which results in a normal amount of bass and a broad midrange hump in the response curve. The newer version allows modification to flatten the response; the earlier version can only produce bass with extremely heavy bass equalization.

The only way to tell the two versions apart is earpad shape because this is the only change. Everything else is the same. Sadly, the new earpads have proven difficult to get hold of through normal retail and online channels.

Following are some excerpts from Fostex's original T50RP brochure:

Fostex T50RP v2 box

Fostex T50RP v2 box rear

1) By making the pattern of the coil a zigzag pattern, the stiffness of vertical and horizontal directions is well balanced reducing unwanted peaks in high frequencies and resulting in a very natural sound.

2) By using copper foil rather than conventional aluminium foil and by using a base film constructed of polyimide [Kapton or equivalent] instead of conventional polyester, the T50RP superbly handles high sound pressure levels with minimum distortion.

Enlarged view of the pattern of the printed coil

Overall shape of the diaphragm

3) The design of the magnet and its neodymium construction means that the RP-Series realizes three-time more flux density than usual. In addition flux vectors are efficiently distributed inside the circuit with minimal leakage.

Magnetic circuit photograph (one side)

Magnetic flux conceptual drawing

4) To minimize unwanted resonances and to increase rigidity, the drive unit is securely adhered to the housing by using a joint pole which has anti-vibration material bonded on its contact surfaces. High sound pressure levels are handled with ease.

General Description of the Sound

Fostex T50RP driver with damper removed

Unmodified, the T50RP with the revised earpads sounds warm and slightly bassy with a lower midrange hump. The treble is a bit rolled off at the very top though very detailed. After modification (damping with felt and cotton) the bass becomes tight and fast and the rest of the frequency range is much flatter. Mids still have a warm and fluid coloration to them that is in no way unpleasant to my ears.

Modifications

Faust3D Modification

Fostex T50RP Faust3D suggested modification

Fostex T50RP Faust3D modification is outlined in the below diagram. After this modification the sound is more balanced and transient response is greatly improved, lower frequencies tighten as ear-cup resonances are reduced.